Indeed it's a 101. Thanks for your comments. The only one I would really disagree with is "always represent more than one data series". That's really tough to represent multiple series on one single chart and manage to keep it immediatly readable.
Certainly a chart should be readable, but I think it's okay to ask for a few moments of careful study. I'm much more interested in a chart that provides some context or basis for comparison, if not with several series than with small multiples or a representation of the general distribution.